For many, the investigation will stop there. No need to explore personal motives, out-of-control grievances or distorted political anger. The mere mention of mental illness is explanation enough. This presumed link between psychiatric disorders and violence has become so entrenched in the public consciousness that the entire weight of the medical evidence is unable to shift it. Severe mental illness, on its own, is not an explanation for violence, but don't expect to hear that from the media in the coming weeks.

Rates of women who are opting for preventive mastectomies, such as Angeline Jolie, have increased by an estimated 50 percent in recent years, experts say. But many doctors are puzzled because the operation doesn't carry a 100 percent guarantee, it's major surgery -- and women have other options, from a once-a-day pill to careful monitoring.

Seena Fazel is an Oxford University psychiatrist who has led the most extensive scientific studies to date of the links between violence and two of the most serious psychiatric diagnoses—schizophrenia and bipolar disorder, either of which can lead to delusions, hallucinations, or some other loss of contact with reality. Rather than looking at individual cases, or even single studies, Fazel's team analyzed all the scientific findings they could find. As a result, they can say with confidence that psychiatric diagnoses tell us next to nothing about someone's propensity or motive for violence.

A 2009 analysisof nearly 20,000 individuals concluded that increased risk of violence was associated with drug and alcohol problems, regardless of whether the person had schizophrenia. Two similaranalyseson bipolar patients showed, along similar lines, that the risk of violent crime is fractionally increased by the illness, while it goes up substantially among those who are dependent on intoxicating substances. In other words, it's likely that some of the people in your local bar are at greater risk of committing murder than your average person with mental illness.

Of course, like the rest of the population, some people with mental illness do become violent, and some may be riskier when they're experiencing delusions and hallucinations. But these infrequent cases do not make "schizophrenia" or "bipolar" a helpful general-purpose explanation for criminal behavior. If that doesn't make sense to you, here's an analogy: Soccer hooligans are much more likely to be violent when they attend a match, but if you tell me that your friend has gone to a soccer match, I'll know nothing about how violent a person he is. Similarly, if you tell me your friend punched someone, the fact that he goes to soccer matches tells me nothing about what caused the confrontation. This puts recent speculation about the Arizona suspect in a distinctly different light: If you found evidence on the Web that Jared Lee Loughner or some other suspected killer was obsessed with soccer or football or hockey and suggested it might be an explanation for his crime, you'd be laughed at. But do the same with "schizophrenia" and people nod in solemn agreement. This is despite the fact that your chance of being murdered by a stranger with schizophrenia is so vanishingly small that a recent studyof four Western countries put the figure at one in 14.3 million. To put it in perspective, statisticsshow you are about three times more likely to be killed by a lightning strike.

The fact that mental illness is so often used to explain violent acts despite the evidence to the contrary almost certainly flows from how such cases are handled in the media. Numerous studiesshow that crimes by people with psychiatric problems are over-reported, usually with gross inaccuracies that give a false impression of risk. With this constant misrepresentation, it's not surprising that the public sees mental illness as an easy explanation for heartbreaking events. We haven't yet learned all the details of the tragic shooting in Arizona, but I suspect mental illness will be falsely accused many times over.

A hearse carrying the remains of U.S. District Judge John Roll arrives at the St. Elizabeth Ann Seton Church before his funeral on in Tucson, Ariz., Friday, Jan. 14. Roll was killed in the Jan. 8 shooting that left six dead and wounded 13, including U.S. Rep. Gabrielle Giffords.
(Morry Gash / AP)
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Mary Kool holds a single red rose outside the St. Elizabeth Ann Seton Church where the funeral of U.S. District Judge John Roll was to take place.
(Eric Thayer / Reuters)
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A flag recovered from ground zero is raised during funeral service for 9-year-old Christina Taylor Green at the St. Elizabeth Ann Seton Church in Tucson, on Thursday, Jan. 13. Green was the youngest victim of the shooting rampage. Green was born on Sept. 11, 2001.
(Mamta Popat / EPA)
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Left to right, Roxanna and John Green, mother and father of Christina Taylor Green, and their son Dallas Green, arrive at St. Elizabeth Ann Seton Church for her funeral in Tucson on Thursday.
(Mamta Popat / Pool via Reuters)
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People dressed as angels line the street leading to the St. Elizabeth Ann Seton Church where the funeral for Christina Taylor Green was to take place in Tucson on Thursday. Hundreds, dressed in white, lined the streets for more than a quarter mile of the funeral procession.
(Mike Segar / Reuters)
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John Green kisses his son Dallas on the head as the family follows the casket of Christina Taylor Green at her funeral mass in Tucson, on Thursday. At left is Christina's mother Roxanna and at right is Camden Grant, Christina's godmother's son.
(Rick Wilking / Pool via AP)
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Cindy and John McCain listen during the funeral service for shooting victim Christina Taylor Green in Tucson on Thursday.
(Greg Bryan / Pool via Reuters)
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A woman holds the service program from the funeral for 9-year-old Christina Taylor Green outside St. Elizabeth Ann Seton Church in Tucson on Thursday.
(Mike Segar / Reuters)
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President Barack Obama speaks at the University of Arizona's McKale Memorial Center during the memorial service for victims of the shootings in Tucson. Obama told the crowd on Wednesday, Jan. 12, that Rep. Gabrielle Giffords had opened her eyes for the first time since being shot in the head during the attack on Jan. 8. Six people were killed and 13 wounded by the lone gunman.
(Jewel Samad / AFP - Getty Images)
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Ron Barber, 65, district director for Rep. Gabrielle Giffords, is visited by Giffords aide Daniel Hernandez in his hospital room on Jan. 9. Hernandez rushed to Gifford's aid after she was shot. Hernandez said that while he held the wounded Giffords, he asked another bystander to put pressure on Barber's wounds. He also asked Barber for his wife's phone number and then shouted it out to someone so that Barber's wife, Nancy, could be informed of the shooting.
(Gabrielle Giffords' Office / Reuters)
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President Barack Obama and First Lady Michelle Obama observe a moment of silence with White House staff members on the South Lawn of the White House in Washington on Jan. 10.
(Jewel Samad / AFP - Getty Images)
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Congressional staff observe a moment of silence to honor victims of the assassination attempt on Rep. Gabrielle Giffords on the steps of the Capitol in Washington.
(Michael Reynolds / EPA)
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Rachel Crabb, 5, holds hands with teachers, parents and other students during a moment of silence for her slain schoolmate, Christina Taylor Green, at Mesa Verde Elementary School on Jan. 9.
(John Moore / Getty Images)
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Candles are lit on Sunday at a makeshift memorial outside University Medical Center in Tuscon, Ariz., for those killed or wounded during the attack on Rep. Gabrielle Giffords .
(John Moore / Getty Images)
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Six balloons representing the six people killed in Saturday's shooting spree, as part of a prayer vigil.Rep. Gabrielle Giffords battled for her life on Sunday after an assailant shot her in the head and killed six others in a rampage that has launched a debate about extreme political rhetoric in America.
(Eric Thayer / Reuters)
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The American flag flies at half-staff on the U.S. Capitol in Washington, on Jan. 9. In a brief statement Sunday morning, House Speaker John Boehner said flags on the House side of the Capitol in Washington will be flown at half-staff to honor the slain aide, Gabe Zimmerman, of Rep. Gabrielle Giffords. Thirty-year-old Zimmerman was among six killed Saturday.
(Manuel Balce Ceneta / AP)
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Emergency personnel use a stretcher to move Rep. Gabrielle Giffords after she was shot in the head outside a shopping center in Tucson on Saturday.
(James Palka / AP)
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Ernie Freuler fights back tears as Ray Lilley takes photos of the scene outside the office of Rep. Gabrielle Giffords after she was shot in the head by a gunman who opened fire outside a grocery store, Saturday, Jan. 8, in Tucson, Ariz.
(Chris Morrison / AP)
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A law enforcement officer stands outside the home of Jared L. Loughner, identified by federal officials as the suspect arrested in connection with the shooting of U.S Representative Rep. Gabrielle Giffords in Tucson, Ariz., Jan. 8.
(Eric Thayer / Reuters)
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People gather for a candlelight vigil for the victims of the shooting in Arizona at the steps of Capitol Hill in Washington, D.C., on Saturday Jan. 8.
(Jose Luis Magana / AP)
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Vera Rapcsak and others hold signs outside the office of Rep. Gabrielle Giffords on Saturday after she was shot while meeting constituents.
(Chris Morrison / AP)
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Emergency personnel attend to a shooting victim outside a shopping center in Tucson, Ariz. on Saturday, Jan. 8, where Rep. Gabrielle Giffords and others were shot as the congresswoman was meeting with constituents. Rep. Giffords, 40, a Democrat, took office in January 2007, emphasizing issues such as immigration reform, embryonic stem-cell research, alternative energy sources and a higher minimum wage. The gunman shot Giffords in the head, seriously wounding her, and killed six other people in a shooting rampage at a public meeting in Tucson on Saturday. Giffords was airlifted to a hospital in Tucson where she underwent surgery. One of the doctors who treated her said he was optimistic about her recovery.
(James Palka / AP)
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A woman places flowers by the office of Rep. Gabrielle Giffords on Capitol Hill in Washington on Saturday after she was shot in Tucson by a gunman who opened fire, killing six people, including a U.S. district judge, John M. Roll.
(Nicholas Kamm / AFP - Getty Images)
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In this photo provided by The White House, President Barack Obama talks with Arizona Gov. Jan Brewer about the shooting.
(Pete Souza / AP)
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Emergency personnel at the scene where Giffords and others were shot outside a Safeway grocery store in Tucson on Saturday.
(Matt York / AP)
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